I realize that I'm probably on the verge (or well past the point) of being considered a 37 Signals "fanboi". I've written already about how much I like Backpack. I still use it every single day, it's one of very few things I pay a monthly fee for and never regret it. It is my homepage on all my personal computers. A few weeks ago when I started seeing some of the early information on Highrise I was rather dismissive of it. It seemed like a streamlined, "kiss" version of Salesforce.com. I figure I didn't have a need for this -- unlike the knob. (Note, CRM in the title here is Customer Relationship Management.) I started using Highrise just to see what it did and explore how the 37 Signals team had built it. It's a great application, incredibly and simply designed. I'd encourage anyone that builds web applications to check it out just to experience the user interface. I decided to give it a go for my "personal business". Things like tax preparation with the accountant, projects being done at the house, etc. I warmed slowly to it, and am really liking it now. Highrise has some great features that make it useful even in solo mode, with only me using it. I never would have thought this type of function would be that useful for personal purposes, but it's pretty nice.
On a side note, I can totally see how a company of 100 or fewer employees would really benefit from Highrise. In fact, the combination of Highrise (customer, vendor management), Basecamp (project management) and Campfire (distributed meetings) fill out most of what a small- to medium-sized company would need for collaboration.